Disk drives store large amounts of digital data. The data is stored on magnetic disks in concentric tracks. The tracks are divided into servo sectors that store servo information and data sectors that store user data. A read/write head reads data from and writes data to the disk. The head includes a read element and write element that may be separate elements or a single integrated element. The head is mounted on an actuator arm assembly that moves the head radially over the disk. Accordingly, the actuator arm assembly allows the head to access different tracks on the disk. The disk is rotated by a spindle motor at high speed, allowing the head to access different data sectors within each track on the disk.
Disk drives include parameters that are dependent on temperature. For example, the write current supplied to the head to sufficiently magnetize the disk such that data is reliably encoded on the disk increases as the temperature decreases. The need for increased write current at reduced temperature results from several factors. For instance, the disk coercivity and thus the magnetic field strength required to magnetize the disk increases as the temperature decreases. In addition, the flying height of the head over the disk increases as the temperature decreases since the air density inside the disk drive increases, and larger write current is required to magnetize the disk due to the increased distance between the head and the disk.
Disk drives have attempted to use a satisfactory write current over anticipated operating temperatures, have been provided with screened heads to eliminate heads that require large write current, and have operated under restricted temperature ranges. However, as data storage densities and data transfer rates increase, disk drive tolerances for variations in written data have decreased. Therefore, a need has emerged to vary the write current in response to temperature changes.
Disk drives have varied the write current with temperature to maintain a desired track width since changes in disk coercivity and flying height result in varying track width. However, this neglects head instability and head deformation that may result from write current that is inappropriate for a given temperature.
Head instability arises from high write current and elevated temperature, thereby causing temporary or permanent inability of the head to reliably and accurately read data from the disk. In particular, the read element suffers from write induced instability due to pinning of magnetic domains and becomes insensitive to magnetic fields on the disk.
Head deformation also arises from high write current and elevated temperature. In particular, the write element suffers from pole tip protrusion and is more likely to contact with the disk. Head-disk contact can damage the head and the disk, misposition the head and cause data errors.